1. Field of the Invention
The present invention relates to a method and a device for detecting a nucleic acid such as DNA. More specifically, the present invention relates to a method and a device for detecting a nucleic acid by removing impurities that are produced in a PCR amplification process of a nucleic acid sample, denaturing the nucleic acid sample by heating, and adsorbing a single-stranded nucleic acid fragment prepared by denaturation onto a gate adsorption layer of a FET-based sensor.
2. Description of the Related Art
Among the many devices used for detecting nucleic acid, including DNAs, RNAs, PNAs (peptide nucleic acids), and other biomolecules, etc., with an electric signal, researches are now actively progressing to develop a transistor-based sensor. Researches are now actively progressing to develop a transistor-based sensor since these can be easily manufactured using a semiconductor process incorporated with an integrated circuit and MEMS (microelectromechanical system) fabrication process. Another advantage of the transistor-based sensor is that it can promptly provide a sensing result through an electrical signal processing.
The most well-known transistor-based sensor used to observe biological processes is a FET-based sensor employing a field-effect transistor (FET). The FET-based sensor is a small scale device, which can be advantageously used for a lab-on-a-chip (LOC) (which spots or diagnoses all types of diseases at once on a small chip), point of care (POC) and on the like testing methods.
A conventional FET-based sensor measures the surface charge density for use in measuring an electrical signal upon a target biomolecule that is adsorbed onto a gate surface.
In order to detect a biomolecule with the FET-based sensor, it is important to prepare a highly pure biomolecule sample. In other words, all impurities in the sample must be removed as much as possible.
For instance, a target nucleic acid for detection normally undergoes an amplification process, such as, for example, polymerase chain reaction (PCR), ligase chain reaction (LCR) and rolling circle amplification (RCA). Such amplification methods generally require the use of a variety of chemicals, e.g., enzymes, salts or monomers for polymerization, which naturally enter a sample during the reaction. These chemical impurities generally have an electric charge and can interfere with the FET-based sensor. Specifically, these chemical impurities can generate unwanted electric noises when nucleic acid in the sample are being detected through the FET-based sensor.
In one attempt to solve the above problem, a PCR product purification kit (from Qiagen) has been developed and is now commercially available. However, the purification kit, and other PCR purification kits, include a chaotropic salt. Therefore, no matter how efficiently impurities like enzymes, dNTP, or primers are removed from a PCR product through the purification kit, the purified sample including an amplified nucleic acid will still contain a considerable amount of the chaotropic salt.
Therefore, if the purification process was carried out in the presence of a chaotropic salt, it is necessary to lower the concentration of the salt by dialysis.